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//
// Comparer
//
// Authors:
// Ben Maurer (bmaurer@ximian.com)
//
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.Runtime.InteropServices;
namespace System.Collections.Generic {
[Serializable]
public abstract class EqualityComparer <T> : IEqualityComparer, IEqualityComparer <T> {
static EqualityComparer ()
{
if (typeof (T) == typeof (string)){
_default = (EqualityComparer<T>) (object) new InternalStringComparer ();
return;
}
if (typeof (IEquatable <T>).IsAssignableFrom (typeof (T)))
_default = (EqualityComparer <T>) Activator.CreateInstance (typeof (GenericEqualityComparer <>).MakeGenericType (typeof (T)));
else
_default = new DefaultComparer ();
}
public abstract int GetHashCode (T obj);
public abstract bool Equals (T x, T y);
static readonly EqualityComparer <T> _default;
public static EqualityComparer <T> Default {
get {
return _default;
}
}
int IEqualityComparer.GetHashCode (object obj)
{
if (obj == null)
return 0;
if (!(obj is T))
throw new ArgumentException ("Argument is not compatible", "obj");
return GetHashCode ((T)obj);
}
bool IEqualityComparer.Equals (object x, object y)
{
if (x == y)
return true;
if (x == null || y == null)
return false;
if (!(x is T))
throw new ArgumentException ("Argument is not compatible", "x");
if (!(y is T))
throw new ArgumentException ("Argument is not compatible", "y");
return Equals ((T)x, (T)y);
}
[Serializable]
sealed class DefaultComparer : EqualityComparer<T> {
public override int GetHashCode (T obj)
{
if (obj == null)
return 0;
return obj.GetHashCode ();
}
public override bool Equals (T x, T y)
{
if (x == null)
return y == null;
return x.Equals (y);
}
}
}
[Serializable]
sealed class InternalStringComparer : EqualityComparer<string> {
public override int GetHashCode (string obj)
{
if (obj == null)
return 0;
return obj.GetHashCode ();
}
public override bool Equals (string x, string y)
{
if (x == null)
return y == null;
if ((object) x == (object) y)
return true;
return x.Equals (y);
}
}
[Serializable]
sealed class GenericEqualityComparer <T> : EqualityComparer <T> where T : IEquatable <T> {
public override int GetHashCode (T obj)
{
if (obj == null)
return 0;
return obj.GetHashCode ();
}
public override bool Equals (T x, T y)
{
if (x == null)
return y == null;
return x.Equals (y);
}
}
}
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